Depends on how many contests you do and win. You won't make much unless you're one of the top pro's. Winning major contests and such. It is not something to get into for the money, That's for sure. You should always have a real job aside from pro bodybuilding until you become a top level competetor(In the top 10 in the olympia and winning a few contests a year). Contracts make you $ too but it depends on who you are. Ronnie Coleman would make more $ for a contract than Bob Chicerillo.
Living on the $ you would make as a 3rd tier(Assuming you did atleast 2 contests a year and have no contracts,Which most 3rd tiers don't have) you would make less than 10,000$ a year.)